1. Field of the Invention
The present invention relates to a conical bearing apparatus used in a motor, and more particularly to a conical bearing apparatus capable of enhancing productivity by removing grinding and lapping steps and reducing the time required in grinding and lapping.
2. Description of the Related Art
Recently, with the improvement of technologies in the information and media industries, such as computer systems, audio systems and video systems, driving motors for various kinds of devices, such as a head driving apparatus of a video tape recorder, an optical polygon driving apparatus of a laser printer, or a camcorder driving motor, need to have a high density and more compact size. In this respect, components of such systems require a more precise performance. Those driving apparatuses require a bearing which is precise and stable, and has a superhigh rotation performance. In compliance with such a need, a hemispheric bearing apparatus, i.e., a dynamic pressure fluid bearing apparatus has been developed which supports both the radial load and thrust load and is suitable to perform the desired superhigh speed rotation.
FIG. 1 is a sectional view of an optical polygon driving apparatus of a laser printer employing a conventional hemispheric bearing. Referring to FIG. 1, the optical polygon driving apparatus includes: an optical polygon 10 for deflecting a laser beam to a photoconductive drum (not illustrated); hemispheric bearing apparatuses 20, 30, 35 and 40 for rotating the optical polygon 10 at a superhigh speed with a minimum friction; rotary power generating apparatuses 50 and 55 which are connected to the hemispheric apparatus and for generating the rotary power; and a lower housing 70 and an upper housing 75 for receiving the above-identified components.
A through hole having a predetermined diameter is formed at the optical polygon 10. To the through hole of the optical polygon 10, a hub 60 is connected. The hub 60 has a shape in which two cylinders 60a and 60b having different diameters are connected. The through hole of the optical polygon 10 is inserted to the cylinder 60a having a smaller diameter. At the cylinder 60b having a larger diameter, a groove 60c having a predetermined diameter and depth is formed.
After the optical polygon 10 is inserted into the cylinder 60a having a smaller diameter, it is located at a projection which is formed at a position where the cylinder 60a having a smaller diameter and the cylinder 60b having a larger diameter are connected, thereby completely contacted by a plate spring 65.
At the hub 60, a bush 40 which has a predetermined height and has a cylindrical shape whose inside is filled is connected. As the diameter of the bush 40 is slightly larger than the groove 60c of the hub 60, it is tightly fitted to the groove 60c. Moreover, at both ends of the bush, a through hole having a predetermined diameter is formed, respectively. The diameter of the through hole is slightly larger than that of a shaft 20 which is fixed at the lower housing.
As shown above, through holes which penetrate each center of both ends of the bush 40 are formed. At the both ends of the bush 40, two hemispheres are located, with their hemispheric surfaces facing each other, and there are hemispheric concaves 30a and 30b each having the same shape as hemispheres 30 and 35 each having a dynamic pressure generating groove (not illustrated) of a spiral shape.
As the shapes of the hemispheric concaves 30a and 30b formed at the bush 40 and the hemispheres 30 and 35 indented on the shaft 20 are the same, in the case that the hemispheres 30 and 35 are fitted to the hemispheric concaves 30a and 30b of the bush 40 closely, a clearance for forming a fluid pressure is not formed between the bush 40 and the hemispheres 30 and 35, and thereby it is impossible to perform the function of the fluid bearing. Accordingly, as it is necessary to have a proper clearance between the bush 40 and the hemispheres 30 and 35, a ring-shaped spacer 40a having a precise height and a predetermined inner and outer diameters are formed at the through hole of the bush 40 so as to have a predetermined clearance between the hemispheres 30 and 35 and the hemispheric concaves 30a and 30b.
At this time, the lower hemisphere 30 and the lower hemispheric concave 30a are completely contacted due to the influence of the gravity. Between the upper hemisphere 35 and the upper hemispheric concave 30b, a clearance is formed.
At the outer surface of the bush 40, a rotor 50 is formed. A stator 55 is located at a predetermined position of the lower housing 70, apart from the rotor 50.
The hemispheres 30a and 30b are processed to have a high sphericity of 0.05 .mu.m, and they are grinded and lapped to have a smooth surface.
The operation of the hemispheric bearing used in a laser scanning motor will be explained, with reference to the drawings.
First, when the power is applied to the stator 55 and then the rotor 50 and the bush start to rotate, the lower hemispheric concave 30a of the bush 40 is lowered in the direction of the gravity by the load of the bush 40, and thereby it is contacted to the lower hemisphere 30 without any clearance.
As shown above, as the lower hemisphere 30 is contacted to the lower hemispheric concave 30a and the upper hemisphere 35 is apart from the upper hemispheric concave 30b, when the bush 40 rotate, the clearance between the upper hemispheric concave 30b and the upper hemisphere 35 is larger than the clearance between the lower hemisphere 30 and the lower hemispheric concave 30a. As a result, as the dynamic pressure becomes larger in the lower hemisphere 30 and the lower hemispheric concave 30a, the lower hemispheric concave 30a is raised from the lower hemisphere 30 by the generated dynamic pressure.
However, as the bush 40 is raised from the lower hemisphere 30, the clearance between the lower hemisphere 30 and the lower hemispheric concave 30a becomes larger, and the clearance between the upper hemisphere 35 and the upper hemispheric concave 30b becomes smaller. As a result, the dynamic pressure formed by the upper hemisphere 35 and the upper hemispheric concave 30b tends to increase.
The bush 40 which is formed between a pair of hemispheres varies the clearance, and it is rotated in an equilibrium state in the clearance where the difference of the dynamic pressure generated in the lower hemisphere and the upper hemisphere coincides with the weight of the rotary body.
However, since the hemispheric bearing must be precisely processed, the lapping process should be performed by a separate lapping machine to achieve the smooth surface. This requires increased time to manufacture the hemisphere, thereby preventing efficient mass production.